Hybrid bearing block for a camshaft

ABSTRACT

A bearing apparatus for mounting a camshaft in a cylinder head of an internal combustion engine may include a bearing element that surrounds a bearing ring in which the camshaft is rotatably mounted or mountable. The bearing element may be made of a first material whose expansion coefficient is greater than an expansion coefficient of a second material of which the bearing ring is made. An outer surface of the bearing ring may include a contour that engages in a form-fitting manner with a mating contour formed on an inner surface of the bearing element that surrounds the bearing ring. The contouring formed by the contour and the mating contour may form retaining structures that brace against one another in instances of thermal expansion.”

The invention relates to a bearing element for mounting a camshaft in the cylinder head of an internal combustion engine, wherein the bearing element surrounds a bearing ring in which the camshaft is rotatably mounted, wherein the bearing element is made of a first material whose expansion coefficient is greater than the expansion coefficient of the second material from which the bearing ring is made. The invention also relates to a system consisting of a bearing element, a bearing ring and a camshaft.

PRIOR ART

Camshafts which are mounted in sliding bearings have been known for a long time and require no particularly high outlay in terms of design. However, since, for weight-reduction purposes, an ever-increasing number of internal combustion engine parts are made of particularly lightweight materials such as aluminum or even plastic, particular attention must be paid to the transitions between the components made of different materials. In the case of the camshafts, for example, the bearing elements are made of lightweight materials while the camshafts themselves are, as ever, made of steel alloys.

As is known, the lightweight materials have greater expansion coefficients (aluminum: longitudinal expansion coefficient α=23.1*10⁻⁶ K⁻¹) than steel alloys, whose longitudinal expansion coefficients are approximately half of this. Indeed, the spatial expansion coefficient γ can even be γ=3*α. Due to these different expansion coefficients of a camshaft which is made of steel and is mounted in a bearing made of aluminum, the bearing play changes as the engine heats up such that the bearing gap increases. As the engine heats up, the increasing bearing gap leads to an accordingly increased oil throughput. In that context, this effect is independent of the design of the bearing, in particular whether this is in the form of a bearing block module or as a conventional mounting in the cylinder head or a guide frame. In that context, it is immaterial whether the bearing channel is split or closed.

DE 10 2012 007 334 A1 discloses a plastic camshaft module as a bearing support, which is cast or injected around separately produced steel bearing rings. However, the bearing rings are not adequately held in the plastic.

The present invention therefore has the object of proposing a bearing element which is of simple construction and is cost-effective to produce, is lightweight and sufficiently stable while having a bearing play, with respect to the camshaft, that is as constant as possible over the entire temperature range of an internal combustion engine, and thus reduces the oil throughput. The object is also to propose a corresponding system consisting of a bearing element and a camshaft.

These objects are achieved with the bearing element as claimed in claim 1 and the system as claimed in claim 7. Advantageous embodiments are described in the respective subclaims.

According to the wording of the claims, the invention makes use of the properties of a material pairing and therefore the different expansion coefficients of the materials from which the bearing element and the bearing ring are made in order to use the different expansions to support the mutual bracing. A particularly preferred material pairing involves making the bearing ring and the camshaft from a steel or a gray cast iron, in particular GJL, while the bearing element surrounding the bearing ring is made of a more lightweight material such as aluminum or a magnesium alloy. In order to achieve even expansion, it is advantageous if the expansion coefficient of the second material, which the bearing ring is made of, is at least approximately identical to that of the material which the camshaft, which is to be accommodated, is made of.

An essential aspect of the invention lies in the particular contouring of the transition surfaces formed between the bearing element and the bearing ring. In that context, the contouring is understood as the pairing of the contour on the bearing ring and the mating contour on the bearing element. According to the invention, both sides of this contouring comprise retaining structures which hold the bearing ring and the bearing element together. According to the invention, these retaining structures are designed such that they make use of the effect of the differential expansion under heating to further strengthen the mutual engagement instead of weakening it. Thus, an expansion leads to ever stronger bracing of the retaining structures. The contouring according to the invention achieves a certain improvement in the adhesion of the inserted bearing ring and a targeted transfer of forces between the bearing ring and the bearing element.

Thus, the system according to the invention encompasses a bearing element which is made of the first material and in which a bearing ring, made of a second material, is held in a form-fitting manner. The camshaft which is rotatably mounted in the bearing ring is another part of the system and is made of a third material. According to the invention, the expansion coefficient of the first material of the bearing element is greater than the expansion coefficient of the second material and of the third material.

According to the invention, the outer surface of the bearing ring is provided with a contour which engages in a form-fitting manner with a mating contour formed on the inner surface, surrounding the bearing ring, of the bearing element, wherein the contouring formed by the contour and the mating contour forms retaining structures which brace against one another in the event of thermal expansion. In that context, the expansion coefficients of the second and third materials are at least approximately identical.

The effect of the optimized hold and of the good transfer of force can for example be achieved by the retaining structures forming undercuts, which can, to a certain extent, compensate for different material expansions. In that context, it is advantageous if the contouring thus formed is recessed into the outer surface of the bearing ring as a structure consisting of recesses, and surrounds the bearing ring in axisymmetric fashion. The mating contour formed on the bearing element then accordingly engages in the recesses.

Alternatively or cumulatively, the retaining structure can also form one or more anchors/anchorages which project into the respective other material. In this case, it is advantageous if the contouring extends out from the outer surface of the bearing ring, such that it rises above the outer surface and forms at least one anchor engaging in the bearing element.

Another possibility involves providing retaining structures consisting of toothings extending in both the axial and circumferential directions, wherein the surfaces can advantageously be roughened by a mechanical or chemical process, for example using the alfin process, thus increasing the surface area.

However, all of these embodiments share the fact that the outer surface of the bearing ring is provided with a contour which engages in a form-fitting manner with a mating contour formed on the inner surface, surrounding the bearing ring, of the bearing element. According to the invention, the contouring formed by the contour and the mating contour is such that it forms retaining structures which brace against one another in the event of thermal expansion.

In addition to improving the retention of the bearing ring in the bearing element, this bracing also ensures that the bearing ring does not widen under heating more than the expansion of the camshaft mounted therein. Thus, the targeted use of the differential thermal expansion of the hybrid material system of the mount that forms the counterpart to the camshaft also achieves a constant bearing play between the camshaft and the bearing ring, and therefore a constant, low consumption of lubricating oil. The hybrid material system also makes it possible to cost-effectively create a simple bearing element which is lightweight and yet sufficiently stable.

In a particularly preferred embodiment, the camshaft mount is of modular overall construction. To that end, it is advantageous if the contoured bearing ring according to the invention is held in a module in the form of a bearing block. Ideally, the bearing ring is integrated by casting into the bearing block, which is in particular made of aluminum or a magnesium alloy.

Since a camshaft module generally comprises two parallel camshafts, it is moreover particularly advantageous if two bearing rings are connected to a common anchor designed as a bridge element, in the form of a “dual bearing plate”. In one advantageous embodiment, the dual bearing plate thus formed is cast into the bearing element. Thus, the hybrid construction according to the invention is applied to double bearing blocks. The particular advantage of this embodiment is that the tooth flank play remains constant irrespective of temperature since the material of the dual bearing plate has the same expansion coefficient as the toothed wheels seated on the camshafts. This reduces noise emissions.

PREFERRED EXEMPLARY EMBODIMENTS OF THE INVENTION

One embodiment of the module according to the invention is explained in greater detail below with reference to the figures, in which:

FIG. 1 shows a bearing ring with undercuts, injected into a bearing block,

FIG. 2 shows the transfer of forces from the bearing block to the bearing ring,

FIG. 3 shows a bearing block with a contoured bearing ring,

FIG. 4 shows a bearing block with an injected bearing ring comprising lateral eyelets,

FIG. 5 shows a bearing block with an injected bearing ring comprising an anchor,

FIG. 6 shows a dual bearing plate injected into the bearing block.

FIG. 1 a shows a separate bearing block 1 which, together with a bearing ring 2 injected or cast therein, forms a mount for a camshaft (not shown) in a cylinder head of an internal combustion engine. The bearing block 1 is cast from aluminum and comprises two screw bores 3 by means of which it is secured to the base of a camshaft module. Also visible is an oil duct 4 in the form of a bore which leads from below, through the bearing block 1 and the bearing ring 2, into the sliding bearing (see also FIG. 1b ). FIG. 1b shows a section through the bearing block 1 of FIG. 1 a. It shows the contour 5 introduced into the outer jacket of the bearing ring 2 with two undercuts 6 that are formed by a raised portion having an M-like profile. The material of the bearing block 1 engages behind the undercuts.

FIG. 2a shows a similar combination of a bearing block 1 and a cast-in bearing ring 2, in a section view. In this case, the contouring is a dovetail recess 6 which is incised into the outer jacket of the bearing ring. FIG. 2b shows the dovetail profile of the recess 6 in detail. Also, the arrows show the force flow of the cooling bearing block 1 on the bearing ring 2. As can be seen, this force flow is radially inward. On heating, the aluminum bearing block 1 expands more than the steel bearing ring 2, resulting in tension in the axial direction.

FIGS. 3a and 3b show a variant embodiment in which there are provided retaining structures in the form of axially extending recesses 7 and a circumferentially extending groove 8. In that context, the surface areas are increased using the alfin process, so as to result in better adhesion.

FIG. 4 shows an embodiment in the cutaway state, in which the retaining structure of the bearing ring 2 forms multiple anchors that reach into the material of the bearing block 1 and are surrounded thereby in form-fitting fashion. In that context, two molded-on eyes 9, which are molded-on on either side of the bearing ring 2 in the screwing plane and are dimensioned such that the bores of the eyelets 9 are in line with the lateral screw bores 3, serve as anchors. If the bearing block is screwed onto the camshaft module by means of screws inserted into the screw bores 3, the screws also pass through the eyelets 9. As is also the case of the embodiment shown in FIG. 3, a circumferentially extending groove 8 is provided in the bearing ring 2 and provides additional stability. It can be seen that this embodiment also has an oil duct 4 that leads into the bearing ring 2.

In the exemplary embodiment of FIG. 5, the oil duct 4 is introduced into the anchor 10 that is molded onto the bearing ring 2 and projects vertically downward. In that context, another axial protrusion 11, which is undercut by the material of the bearing block, can be provided at the upper end of the bearing ring 2 as shown in FIG. 5.

In the exemplary embodiment of FIG. 6, two bearing rings 2 are connected via a common anchor in the form of a bridge element 12, and thus form a “dual bearing plate” 13. The dual bearing plate formed in this manner is again cast into the bearing element 1.

LIST OF REFERENCE SIGNS

1 Bearing block

2 Bearing ring

3 Screw bore

4 Oil duct

5 Contour

6 Undercuts

7 Recesses

8 Groove

9 Eyelet

10 Anchor

11 Protrusion

12 Bridge element

13 Dual bearing plate 

1.-8. (canceled)
 9. A bearing apparatus for mounting a camshaft, the bearing apparatus comprising: a bearing block including two screw bores by way of which the bearing block is securable to a base of a camshaft module, the bearing block further including an oil duct; and a bearing ring in which a camshaft is rotatably mounted or mountable, the bearing ring being injected or cast into the bearing block, wherein the bearing ring includes an outer surface having a contour that is adjacent to the bearing block and retains the bearing ring within the bearing block, wherein the bearing ring receives oil from the oil duct.
 10. The bearing apparatus of claim 9 wherein the contour of the outer surface of the bearing ring comprises two undercuts that are formed by a raised portion having an “M”-like profile.
 11. The bearing apparatus of claim 9 wherein the contour of the outer surface of the bearing ring is configured as a dovetail recess.
 12. The bearing apparatus of claim 9 wherein an expansion coefficient of the bearing block is greater than an expansion coefficient of the bearing ring.
 13. The bearing apparatus of claim 9 wherein the outer surface of the bearing ring comprises a retaining structure to improve a connection between the bearing ring and the bearing block.
 14. The bearing apparatus of claim 13 wherein the retaining structure comprises an axially-extending recess.
 15. The bearing apparatus of claim 13 wherein the retaining structure comprises a circumferentially-extending groove.
 16. The bearing apparatus of claim 13 wherein the retaining structure comprises anchors that extend into the bearing block and are surrounded by the bearing block in form-fitting fashion.
 17. The bearing apparatus of claim 13 wherein the retaining structure comprises an anchor that extends into and is surrounded at least partially by the bearing block, wherein the anchor comprises an oil duct.
 18. The bearing apparatus of claim 9 wherein the bearing ring comprises two lateral eyelets that have bores that overlap with the two screw bores of the bearing block.
 19. The bearing apparatus of claim 9 wherein the bearing ring is a first bearing ring, the bearing apparatus further comprising a second bearing ring, wherein the first and second bearing ring are connected by a bridge element that is secured in the bearing block.
 20. A bearing apparatus for mounting a camshaft in a cylinder head of an internal combustion engine, the bearing apparatus comprising: a bearing element that is comprised of a first material that has a first expansion coefficient, a bearing ring in which a camshaft is rotatably mounted or mountable, the bearing ring comprised of a second material having a second expansion coefficient, wherein the first expansion coefficient is greater than the second expansion coefficient, wherein the bearing ring is surrounded by the bearing element; and wherein the bearing ring includes an outer surface with a contour that engages in a form-fitting manner a mating contour of an inner surface of the bearing element that surrounds the bearing ring, wherein contour and the mating contour form a retaining structures that brace against one another in an event of thermal expansion.
 21. The bearing apparatus of claim 20 wherein the bearing ring is cast into the bearing element, with the bearing element being configured as a single bearing block.
 22. The bearing apparatus of claim 20 wherein the contour is recessed into the outer surface of the bearing ring and surrounds the bearing ring in axisymmetric fashion, wherein the mating contour engages in the recessed contour.
 23. The bearing apparatus of claim 20 wherein the contour is raised above the outer surface of the bearing ring and forms an anchor that engages in the bearing element.
 24. The bearing apparatus of claim 23 wherein the bearing ring is a first bearing ring, the bearing apparatus further comprising a second bearing ring, wherein the first and second bearing rings are connected by a common anchor configured as a bridge element and form a dual bearing plate that is cast into the bearing element.
 25. The bearing apparatus of claim 20 wherein the second expansion coefficient is approximately equal to or greater than an expansion coefficient of material of which the camshaft is comprised.
 26. A system comprising: a bearing element comprised of a first material having a first expansion coefficient; a bearing ring comprised of a second material having a second expansion coefficient, wherein an outer surface of the bearing ring includes a contour that engages in a form-fitting manner with a mating contour of an inner surface of the bearing element such that the bearing element holds the bearing ring in a form-fitting manner, with the contour and the mating contour forming retaining structures that brace against one another in an event of thermal expansion; and a camshaft that is rotatably mounted in the bearing ring and is made of a third material having a third expansion coefficient, wherein the first expansion coefficient is greater than the second and third expansion coefficients.
 27. The system of claim 26 wherein the second and third expansion coefficients differ by less than 5%.
 28. The system of claim 26 wherein the bearing ring and the camshaft are comprised of a steel or a gray cast iron, wherein the bearing element is comprised of aluminum or a magnesium alloy. 